Japan was unwilling to surrender for a long time even though Japanese cities got bombed on a near daily basis near the end of the war. The US gambled on, for a lack of a better word, the wow-factor of the atomic bomb. They guessed correctly that Japan’s leaders would assume that there’s no way in hell the US could produce another one of these “special” bombs. They dropped the second one to basically say: “Hey, we got a huge stockpile of these things so we can do this as long as you like”. Or to put it simply: It was a show of force. When Nagasaki got hit Japanese leaders were in a council meeting about the Hiroshima bombing and the Soviet’s declaration of war on Japan and even after the news arrived in Tokyo half the cabinet was still insistent on their own terms of surrender. They didn’t know how many more bombs America had and that fear played a huge part in Hirohito’s decision to end the war after more than 14 hours of debate that day.

[–] Fried_out_Kombi@lemmy.world 3 points 1 year ago

Exactly. Simply having enough fissile material for a bomb was a huge limiting factor for building a bomb. It took several years of refining for the US to have enough for the Trinity Test, Fat Man, and Little Boy. Any physicists in Japan at the time had to have known that fissile material was a limiting factor, given that the theoretical concept of an atomic bomb was well-known physics by the time. The second bomb was to prove Japan couldn't count on the US having exhausted all their fissile material on the first bomb.

[–] queermunist@lemmy.ml 3 points 1 year ago* (last edited 1 year ago)

It was a show of force.

Yes, it was, but not for Japan. If they had given Japan more than three days between Hiroshima and Nagasaki to think it over they'd have likely surrendered, but defeating Japan wasn't really the point. It was a show of force for the rest of the world (especially the USSR) to say "we are the new rulers of the world, bow down and submit or we'll glass you too".